Generally, in a vehicle provided with an electric power steering apparatus, steering torque generated in a steering shaft with steering operation is detected by a torque sensor, and an electric current flowing in an electric motor is controlled by a controller according to the steering torque, whereby the electric motor allows the steering shaft to output a required steering assist force (torque) via a speed reducer.
A conventional electric power steering apparatus of this type is disclosed, for example, in Patent Document 1. In this electric power steering apparatus, an electric motor for imparting steering assist force to a steering system and a control unit provided with a controller for controlling an energizing state of the electric motor according to steering torque of the steering system are arranged in proximity to each other. In this case, there are two objects for arranging the electric motor and the control unit in proximity to each other in this manner. A first object is to make the device compact and to save cost for material for achieving cost reduction, by decreasing a length of an electric wiring provided between the two members to the least. A second object is to improve quality of the device by decreasing electric power loss, noise, heat generation, etc. From a viewpoint of these objects, this structure has been employed in many electric power steering apparatuses, in recent years.
Patent Document 1: Japanese Patent Examined Publication No. JP-B-3,638,269